docs: def _publish_connection(self, name=None):
          """Return the connection to publish. If the name is not specified,
          the connection associated with the current message is returned.
  
          :param str name:
          :rtype: rejected.process.Connection
  
          """
          try:
              conn = self._connections[name or self._message.connection]
          except KeyError:
              raise ValueError('Channel {} not found'.format(name))
          if not conn.is_connected or conn.channel.is_closed:
              raise RabbitMQException(conn.name, 599, 'NOT_CONNECTED')
          return conn